Can't get model manifold for 3d printing
Non-manifold doesn't necessarily mean double vertices (although there are quite a lot in your mesh). It could also mean that you have vertices inside your mesh. Import it into blender, tab into Edit Mode, then go to "3D Viewport - Menu - Select - All By Trait - Non Manifold". Try to delete the vertices and then try to verify on shapeways again. 

Your second question: I don't have much experience with printing, but I think your model is way too complex and it also contains ngons.